There are known cellular phones (radio communication apparatuses) that is opened and closed by relatively sliding or rotating their casings. In radio communication terminals, it is important to improve antenna characteristics. For example, Patent Document 1 discloses a case in which antenna characteristics deteriorate when a radio communication terminal approaches a human body, and a technology that prevents the antenna characteristics from deteriorating by providing a first parasitic element longer than the electrical length of an antenna on the front surface side of a casing including a display unit and a second parasitic element shorter than the electrical length of the antenna on the rear surface side of the casing.
In cellular phones whose casings are opened and closed, a problem may arise in that the antenna characteristics of the cellular phones are changed between the opened state and the closed state of the casings. One of the causes of the change in the antenna characteristics of cellular phones is a change in the positional relation of a conductor included in the cellular phones between the opened state and the closed state of the casings. Since cellular phones comprise conductors in a flexible printed circuit (FPC) that is a flexible interconnect substrate interconnecting the casings or in the casings themselves, the positional relation between the casings and that of the folded states of FPC are changed depending on the opened state and the closed state of the casing.
For example, in the case of the FPC that connects the casings each other, the FPC is folded in either the opened or closed state and is extended in a substantially straight shape in the other state. In this case, currents with reverse phases flow in a region in which the FPC is folded and overlaps in a double-sheet shape (hereinafter, referred to as an overlapping region). For this reason, if an overlapping region exists near an antenna device disposed in a casing, each side of the overlapping FPC individually has an influence on the antenna characteristics. Therefore, when the folded state of the FPC is changed by opening or closing the casings, the antenna characteristics change. The change in the antenna characteristics has an adverse effect on communication quality.
On the other hand, Patent Document 2 discloses a technology in which the FPC in the overlapping region is short-circuited by providing a conductor piece fixed to a casing in a block state between the folded FPC and performing capacitance coupling. Thus, an effective length of the facing length between the casing and the FPC is adjusted.
Further, another cause to change the antenna characteristics of a cellular phone is that switching casings between the opened state and closed state changes the positional relation between the conductors such as metal plates of the casings. As will be described in detail later, currents flowing in the casings in the opened state do not interfere with each other. However, since the radio waves radiated from the currents flowing in the casings overlapping with each other in the closed state have reverse phases, the antenna function of a cellular phone deteriorates.